This is a practice piece using Frostwindz "Fantasy Hammer Concept Art" artwork from Deviantart: https://www.deviantart.com/frostwindz/art/Fantasy-Hammer-Concept-Art-594204526
It's a gorgeous design and ended up translating to 3D very easily. I like to think the hammer is not square, but diamond shaped, and I think the way the iron bands are wrapped around support that interpretation.